1. Field of the Invention
The present invention relates to gaskets, and more particularly to gaskets which are formed in-place on a substrate and cure to a have a substantially tack-free surface. Such find use in the production of electronic devices, such as housings for glass, plastic and metal enclosures.
2. Description of the Related Art
There is great commercial interest in preparing devices such as electronic devices which have sealable housing layers enclosing electronic circuits. Often such housing layers sandwich a peripheral gasket for preventing entry of contaminants into the device housing. Typical electronic devices include hand held cell phones, pagers, global positioning systems, personal digital assistants, and the like. These enclose delicate displays, electronic circuits, and similar components, that can be easily damaged during everyday use. Indeed, electronic circuits within the device can be rendered inoperable if debris such as dust particles, enter the device through gaps between adjacent housing layers. Therefore, such electronic devices typically include one or more gaskets or seals between some adjacent components, such as the device housing and the display assembly. These gaskets transfer impact forces to more rugged support frames within the device and away from delicate components, and the same gaskets inhibit debris from entering the device which that could damage electronic circuits. Unfortunately, these gaskets, due to their tight positioning between housing layers, typically make device assembly relatively difficult as it can be difficult to press a panel into a gasket that extends around the perimeter of another panel because of the small clearances between the two panels. If care is not taken during this step, one panel could flatten part of the gasket instead of properly connecting to it, thereby partially rendering the gasket ineffective for preventing debris from entering. Other methods for connecting a gasket to a panel, such as co-molding, typically fail because of different material properties of the two components. In particular, some panels cannot tolerate the high temperatures used in co-molding operations. U.S. Pat. No. 8,508,927 shows one form of a gasket for assembling an electronic mobile device, however, this disclosure employs a preformed gasket which engages a device panel, a spacer and an outer panel. U.S. Pat. No. 6,346,330 describes a low out-gassing UV-cationic formulation which can be used in form in-place gasket materials for electronic devices. International patent publication WO2007/001937 shows a UV-free radical curing form in-place gasket formulation utilizing alkyl(meth)acrylate polymers. U.S. Pat. Nos. 6,787,225 and 6,448,302 show a radiation curable coating which employs a wax, however, gaskets are not contemplated. U.S. Pat. No. 8,400,730 shows multistage gaskets using multiple material types, however, these provide a thick seal.
The present invention solves these problems by first forming and attaching a liquid radiation polymerizable, gasket forming composition onto a substrate, and then curing the liquid composition into a flexible, substantially tack free gasket. Since the gasket is formed in-situ, it adheres onto the first substrate, and is cured to a substantially non-tacky state by radiation polymerization rather than by high temperatures which the electronic device components cannot tolerate. Then a second substrate is removably, non-adhesively positioned onto the first substrate with the gasket between the two substrates. Since the gasket has a substantially non-tacky surface, the second substrate can easily be detached from the first substrate for access to the in-between electric circuits for repairs.